Heretofore, in the field of an image forming apparatus which uses an electrophotographic image forming process, the process cartridge which includes a photosensitive drum s and a developing roller which acts on the photosensitive drum and a developing unit which contains a developer (toner) to be used for the image formation as a unit is known. A developing cartridge type using the developing unit which does not include the photosensitive drum is also known. According to these cartridge types, a maintenance operation of a device can be carried out by the user without a service person, in effect. For this reason, these cartridge types are widely used for the electrophotographic image forming apparatus.
It is also known that a drawer for carrying the process cartridge or the developing cartridge is provided, and the exchange of the cartridge is capable by drawing this drawer from the inside of the main assembly to a predetermined position. According to this technique, the user can supply the developer easily, in effect.
Here, when the image formation is carried out by the image forming apparatus, the developing roller in the developing unit is in the state of being urged toward the photosensitive drum at a predetermined pressure. In a contact-type developing system in which the developing roller is contacted to the photosensitive drum during the developing operation, an elastic layer of the developing roller is in contact to a surface of the photosensitive drum at the predetermined pressure.
Therefore, when the developing unit is used for a long term in the state that it is mounted to the main assembly of the apparatus, the elastic layer of the developing roller may be deformed. This will result in occurrence of non-uniformity in the image by the developing operation. In addition, since the developing roller is in contact with the photosensitive drum, the developer is deposited on the photosensitive drum from the developing roller unnecessarily. Furthermore, since the photosensitive drum and the developing roller are contacted with each other and rotated even when the developing operation is not carried out, and therefore, the deterioration of the developer and the developing roller is accelerated as the case may be.
In order to suppress the acceleration of the deterioration, Japanese Laid-open Patent Application 2007-213024) discloses a mechanism by which the developing roller is spaced from the photosensitive drum when the image formation is not carried out.
In such a prior-art, a member (movable member) movable between a position for contacting the developing roller to the photosensitive drum and a position for spacing them is provided in a main assembly side of the apparatus. When a drawer member (tray) carrying the cartridge photosensitive drum and the developing roller enters the main assembly of the apparatus, the movable member is in the position away from a movement path of the drawer member. By a door being closed after the drawer member is inserted to a predetermined position in the main assembly of the apparatus, the movable member moves toward the cartridge carried on the drawer member to space the developing roller from the photosensitive drum.
However, in such conventional example, the movable member is provided in the main assembly side of the apparatus. Therefore, when the drawer member is moved into the main assembly of the apparatus, it is required that the movable member is retracted to the position not interfering with the drawer member. In addition, in order to space the developing roller from the photosensitive drum, it is necessary to move the movable member to the position of the cartridge on the drawer member. For this reason, the space is required in the main assembly of the apparatus in order to permit the movement of the movable member from the main assembly side of the apparatus to the cartridge position in the drawer member. This impedes downsizing of the main assembly of the apparatus.